feat(plugin): ship the agents from a single root agents/ directory

Move .claude/agents/ and server/data/agent-templates/ship-feature-lane/
into one agents/ at the repo root — which IS the plugin root, so all five
agents now ship with the ccam plugin as ccam:<name>, the same way skills
already do.

The two pipeline agents were byte-identical copies in both places; that
duplication is gone. `ccam lanes agents install` now reads them straight
from agents/, so the per-lane copy in <lane>/.claude/agents/ still gives
the bare `subagent_type: qc-local` the ship-feature-lane skill prefers.
Skill and docs record both names: bare inside a lane, ccam: as fallback.

server/lib/lane-agents.js

@@ -1,7 +1,10 @@
 /**
  * @file Installs the ship-feature-lane pipeline's agent templates
  * (qc-local, senior-gate-reviewer) into a lane's own .claude/agents/, so a
- * driving session can launch them by subagent_type. Plain file I/O except
+ * driving session can launch them by the BARE subagent_type name. Source is
+ * the repo's own `agents/` — the same files the ccam plugin ships, where
+ * they resolve as `ccam:qc-local`; installing them into the lane is what
+ * makes the unprefixed name work there too. Plain file I/O except
  * for one git call — resolving where a worktree lane's shared info/exclude
  * actually lives, the same git-dir/git-common-dir distinction E2's
  * lane-sync.js had to get right for info/attributes.
@@ -12,7 +15,7 @@ const fs = require("node:fs");
 const path = require("node:path");
 const { git } = require("./worktree");
 
-const TEMPLATE_DIR = path.join(__dirname, "..", "data", "agent-templates", "ship-feature-lane");
+const TEMPLATE_DIR = path.join(__dirname, "..", "..", "agents");
 const TEMPLATE_FILES = ["qc-local.md", "senior-gate-reviewer.md"];
 const EXCLUDE_LINE = ".claude/agents/";